1. Field of the Invention
The present invention relates to an apparatus and a method for exchanging electrode chips used for resistance welding and, more particularly, to an apparatus and a method for removing used electrode chips from the shanks of the arms of the welding gun of a resistance spot welder and then installing new polished electrode chips on the shanks.
2. Description of the Prior Art
Heretofore, the electrode chips mounted on the shanks of the arms of a conventional resistance spot welder have been exchanged for new ones manually by an operator. When a spot welding is performed on a surface-treated steel sheet, such as galvanized sheet iron, the lifetime of electrode chips are extremely short. Especially, the electrode chips on a robot spot welder are frequency changed, because one welding gun produces tens of welds. Therefore, much labor is needed to exchange electrode chips, thus lowering the productivity. Also, where electrode chips are exchanged for new ones manually, various ancillary equipments for improving the efficiency and the safety of the work, such as falsework, must be provided. This makes the whole welding equipment larger and more expensive. Another method of managing electrode chips consists in polishing the chips while the chips are held to an electrode chip holder. However, where special electrodes which are difficult to polish are used, the polishing operation is carried out unsuccessfully or the polishing accuracy is low. Therefore, defective welds tend to be produced. For this reason, the actual situation is that the management of electrode chips depends on exchange of the chips.
In an attempt to exchange electrode chips without requiring any operator's manual operation, some apparatuses have been proposed. For example, an apparatus disclosed in Japanese Utility Model Laid-Open No. 41,482/1986 has a tool for withdrawing electrode chips. The front end of this tool is shaped like a wedge. An apparatus disclosed in Japanese Utility Model Laid-Open No. 41,483/1986 has an electrode chip-withdrawing tool making use of leverage.
When the automatic electrode chip exchange apparatus disclosed in Japanese Utility Model No. 41,482/1986 or 41,483/1986 is used, it is possible to withdraw electrode chips by a mechanical force without requiring an operator's manual operation. However, since a wedge or leverage is employed, the electrode chip-withdrawing tool must be caused to move a large stroke to obtain a sufficient force to withdraw electrode chips. Therefore, the apparatus is large in size. Hence, the space and the cost required are increased.